class ListNode{
    public int val;
    public ListNode prev;
    public ListNode next;
    public ListNode(int val){
        this.val = val;
    }
}
public class MyLinkedList {
    public ListNode head;//指向双链表的头节点
    public ListNode last;//指向双链表的尾节点
    //头插法
    public void addFirst(int data) {
        ListNode node = new ListNode(data);
        if (this.head == null){
            this.head = node;
            this.last = node;
        }else{
            node.next = this.head;
            this.head.prev = node;
            this.head = node;
            return;
        }

    }




    //尾插法
    public void addLast(int data) {
        ListNode node = new ListNode(data);
        if (this.head == null){
            this.head = node;
            this.last = node;
        }else {
            this.last.next = node;
            node.prev = this.last;
            this.last = node;
        }
    };



    //任意位置插入,第一个数据节点为0号下标
    public ListNode searchIndex(int index){
        ListNode cur = head;
        while (index != 0){
            index--;
            cur = cur.next;
        }
        return cur;
    }
    public void addIndex(int index,int data) {
        ListNode node = new ListNode(data);
        if (index < 0 || index > size()){
            return;
        }
        if (index == 0){
            addFirst(data);
            return;
        }
        if (index == size()){
            addLast(data);
            return;
        }
        ListNode cur = searchIndex(index);
        node.next = cur.prev.next;
        cur.prev.next = node;
        node.prev = cur.prev;
        cur.prev = node;

        return;
    }



    //查找是否包含关键字key是否在单链表当中
    public boolean contains(int key) {
        ListNode cur = this.head;
        while (cur != null){
            if (cur.val == key){
                return true;
            }
            cur = cur.next;
        }
        return false;
    }



    //删除第一次出现关键字为key的节点
    public void remove(int key) {
        ListNode cur = this.head;
        while (cur != null){
            if (cur.val == key){
                if (cur == head){
                    head = head.next;
                    if (head != null){
                        head.prev = null;
                    }else{
                        last = null;
                    }
                }else{
                    cur.next = cur.prev.next;
                    if (cur.next != null){
                        //中间位置
                        cur.next.prev = cur.prev;
                    }else{
//                        last = cur.prev;
                        last = last.prev;
                    }
                }
                return;
            }
            cur = cur.next;
        }

    }



    //删除所有值为key的节点
    public void removeAllKey(int key){
        ListNode cur = this.head;
        while (cur != null){
            if (cur.val == key){
                if (cur == head){
                    head = head.next;
                    if (head != null){
                        head.prev = null;
                    }else{
                        last = null;
                    }
                }else{
                    cur.next = cur.prev.next;
                    if (cur.next != null){
                        //中间位置
                        cur.next.prev = cur.prev;
                    }else{
//                        last = cur.prev;
                        last = last.prev;
                    }
                }
            }
            cur = cur.next;
        }

    }


    //得到链表的长度
    public int size() {
        ListNode cur = this.head;
        int count = 0;
        while (cur != null){
            cur = cur.next;
            count++;
        }
        return count;
    };

    //打印链表
    public void display() {
        ListNode cur = this.head;
        while (cur != null){
            System.out.print(cur.val + " ");
            cur = cur.next;
        }
        return;

    }

    //清除链表
    public void clear() {
        ListNode curNext = head.next;
        while (head != null){
            head.prev = null;
            head.next = null;
            head = curNext;
        }
        last = null;
    }

}
